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Photovoltaic technologies use semiconductors to trap the son's light and convert it to electricity. Such solar power is already being used to run all sorts of devices, from calculator to the Hubble Telescope in outer space. These accomplishments show that harnessing solar power is possible, but it remains expensive and in efficient. Scientists are still trying to find ways to make solar power a more widely used energy source. It is a big challenge, but many believe that the future of our planet depends on it.
光电技术利用半导体捕获太阳光能，然后把太阳光能转换成电能。这类太阳能已应用在诸如计算机和哈伯太空望远镜等各种装置中。 上述各项应用成果均证明了太阳能是可以加以利用的，只是还很昂贵，而且成效还不够明显。科学家们至今仍在设法充分利用太阳能。虽然这是一大挑战，但是许多人都认为地球的未来就靠太阳能了。
Perhaps you have a big test coming up and you are feeling nervous. These days, it is pass or perish, so you know you have got to do well. The pressure is on, so you may be losing sleep and the ability to concentrate. How can you deal with the stress, study effectively, and take the test with confidence? Maybe you should try meditation.
也许你正为了明天的大考感到紧张。现在，不是通过，就是完蛋，所以你知道你一定得考好。压力就在那里，你也许就会睡眠不足或无法集中精神。该怎样面对压力，有效地学习，以及信心十足地迎接考试呢?或许你该试试冥想。
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